The present invention relates to a device for actuating an equipment, associated with a drill string lowered in a well, and in which a drilling fluid whose basic function is to provide all the conventional drilling functions circulates. The actuating device according to the invention uses directly the hydraulic energy of the pressure of the circulating drilling fluid for actuating the equipment.
In the oil drilling field, it is often necessary to actuate equipment or tools incorporated in a drill string lowered in a wellbore. This may notably be the case for carrying out controlled directional drillings, exploratory measuring or testing operations or various operations for fitting up production wells.
The prior art mentions several well-known methods for actuating bottomhole equipment. They may consist in pumping tools into the pipe which, once they have reached the level of the equipment, activate it. Instead of pumping, a ball or an equivalent may be dropped into the drill string. These conventional methods present notably the drawback of sealing totally or, at best, temporarily the inner channel of the string, and therefore of requiring a more or less long pumping stop. Now, in drilling, it is always very dangerous not to keep the drilling fluid circulating. In fact, when the upward circulation of the fluid in the well-string annulus is too low, or even zero, there are risks of destabilization of the walls. Moreover, the cuttings being no longer taken up to the surface, they tend to settle and are likely to jam the string.
For all these reasons, technical development turned towards the use of other types of actuation. The action of weight on the tool, of the rotating speed or a combination of both may be used. But, in this case, constructions are very complex and little reliable for checking the control of these drilling parameters.
Patent EP-251,543-A for example is well-known, in which the actuation of a variable geometry stabilizer is achieved by weight on the tool. But the actuating system requires the action of an axial force up to a critical value with no positive locking in a determined position. The user is sometimes faced with error risks concerning knowledge of the position of the equipment. Besides, the weight on the tool is a parameter linked to the drill bit and has a direct influence on the drilling performance, so users do not wish to be limited in the use of this force for anything else than drilling progress.
The device of the present invention does not interfere at any time with the drilling parameters, be they hydraulic or mechanical.
Patent application EP-376,811 mentions a known actuating device comprising a needle-choke system using the hydrodynamic action of the drilling fluid circulation. This document describes the use of a flow rate increase for generating a pressure difference between upstream and downstream from the device sufficiently high for obtaining the actuation. It is obvious that, in this document, the pressure drops downstream from the device reduce the activation force.
On the contrary, in the present invention, all the pressure drops in the string downstream from the device are active for the actuation. This represents a definite advantage since these pressure drops always have sizeable values considering the indispensable presence of bits restricting the passageway, notably a drill bit. The necessary level of activation energy may thus be obtained more easily while remaining in normal operating conditions, which practically suppresses all the interferences with the wellbore surroundings.
In the prior art, which may be illustrated by patent application EP-376,811 cited above, inner mechanisms, notably activation, indexing and locking mechanisms, impose a specific lubrication of the parts. They must therefore be tight in relation to the presence of a fluid under pressure such as the drilling fluid. All these constraints are suppressed by the invention which uses directly the drilling fluid without any other buffer or intermediate fluid.